The present invention is directed to a crane control apparatus for a crane where a load is suspended on a crane cable from a cable suspension point of the crane.
For the control of the crane, exact information on the position and/or the velocity of the load is of great importance. However, this position and/or load velocity of the load can usually not be measured directly, but has to be calculated from measurements that do not directly describe the load position and/or load velocity but related quantities.
For example, in many crane control apparatuses, the cable angle and/or the cable angle velocity is measured by a sensor, from which the load position and/or velocity is calculated. For example, a gyroscope located on a cable follower can be used for measuring cable angle velocity.
However, because of measurement noise and other uncertainties, a purely kinematic model for calculating the position and/or velocity of the load from the sensor input of the sensor is often insufficient for providing the exactness required by usual crane control applications.
Therefore, state observers have been used for estimating at least the position and/or velocity of the load from the sensor input by using a physical model of the load suspended on the crane cable. An example of such a system is shown in DE 100 641 82.
Such observers usually use the cable angle and/or the cable angle velocity as state variables, as this simplifies calculations of the expected measurement signals of the sensors, which relate to the same quantities. The load position and/or velocity is then derived from these state variables.